1. Field of the Invention
The present invention relates to a communication method, apparatus and system, and more particularly to an ultra wide-band (UWB) communication apparatus, system and method employing multiple pulses coupled with multiple delays.
2. Description of Related Art
In a multiple access UWB communications system, users transmit information independently and concurrently over a shared channel. The received signal is therefore a superposition of all user signals with added channel noise. There has been extensive research in separating multiple users in a multiple access UWB system using time division multiple access (TDMA) or code division multiple access (CDMA), Pulse Amplitude Modulation (PAM) and Pulse Position Modulation (PPM) techniques. PAM modulation encodes the data bits based on different levels of power (amplitude) in short duration pulses. In PPM modulation, signals are pseudo randomly encoded based on the position of transmitted pulse trains by shifting the pulses in a predefined window in time. PPM transmitted signals are usually demodulated and recovered with template matching at the receiver. The two main problems associated with these methods are the need for stringent synchronization and the increase in multiple access interference (MAI) as the number of channels increases.
A modulation technique called Transmitted-Reference (TR), characterized by the transmission of a pair of pulses separated by a unique delay to represent data bits, has been utilized to address synchronization problems. This technique sends the same pulse twice through an unknown channel where both pulses are similarly distorted so that the detection of the transmitted pulses becomes easier with an autocorrelation receiver without the synchronization challenges that exist in other conventional approaches. Although this technique has addressed the synchronization problem, the MAI concern still exists due to the fact that a single UWB pulse shape is used for all channels.
Such a multiple access modulation technique to address synchronization problems is described in U.S. Patent No. 2001/0053175, entitled “Ultra-Wideband Communications System,” to Hoctor et al., patented Dec. 20, 2001, including the following: “[t]he present invention consists of the combination of two chief features and innovation surrounding each of them. The first of these is known in the art as transmitted-reference (TR). The TR technique is defined as the transmission of two versions of a wideband carrier, one modulated by data and the other unmodulated. The second feature of the present invention is a type of multiple access scheme called ‘delay hopping’. The term ‘delay hopping’ refers to a multiple access technique that is related to delay modulation in the way that ‘frequency hopping’ is related to frequency modulation. Our new system has high immunity to narrow-band interference by virtue of both the delay-hopping (DH) feature and the use of more than two pulses in the TR transmission.”
Conventional ultra wideband communication systems do not disclose a multiple pulse, multiple delay (MPMD), multiple access system that samples the zero and multiple non-zero lags of received autocorrelated pulses to produce optimal high performance channelization for multiple users.
Accordingly, a need exists for an ultra wideband communication channelization method and system for transmission and reception of multiple sampled autocorrelated ultra-wideband pulses in a multiple access communications format.